This invention relates to a ferrule for optical connectors.
Generally, the ferrule for optical connectors is used to connect optical fibers directly with each other. As shown in FIG. 7, a conventional ferrule contains an optical fiber inserting hole 101 formed through a ferrule body 100 in its axial direction and an optical fiber inserted into the optical fiber inserting hole 101 is fixed therein by an adhesive. An excessive portion of the optical fiber protruding from each end of the ferrule body 100 is cut off and the cut portion thereof is finished to a mirror state so as to be used as a connecting end. By bringing this connecting end into contact with that of other ferrule body constructed in the same manner, the optical fibers are directly connected with each other.
Because the optical fibers are directly connected with each other through the ferrule as described above, the optical fiber must be firmly fixed to the interior of the optical fiber inserting hole 101 in the ferrule with an adhesive so as to have a predetermined fixing strength. Thus, this fixing strength is closely related to a length L of the optical fiber inserting hole 101 and the longer the length, the larger the fixing strength of the optical fiber in the optical fiber inserting hole 101 is. Usually, that length L is often selected to be about 10 mm.
However, if the length of the optical fiber inserting hole 101 is prolonged like this, the following difficulties may occur in processing of the optical fiber. That is, the linearity of the optical fiber inserting hole 101 cannot be easily obtained. Further, hole processing for making the optical fiber inserting hole 101 becomes difficult and it takes very long to process the internal surface of the optical fiber inserting hole 101. So that, a funnel type optical connector ferrule as shown in FIG. 8 has been proposed. This optical fiber inserting hole is constructed so as to have two steps, a large-diameter hole 102 and a small-diameter hole 103. By holding an optical buffered fiber by the large-diameter hole 102, the length LN of the small-diameter hole 103 for fixing the optical fiber is shortened.
Although the tunnel type ferrule can solve the problem of a difficulty in processing by shortening the length LN of the small-diameter hole 103 in which the optical fiber is to be fixed, a sufficient fiber fixing strength cannot be obtained easily and further a deviation in axis between the large-diameter hole 102 and the small-diameter hole 103 may occur. This often reduce connecting performance of the optical fiber.
That is, this type of ferrule is processed by centering in which the external diameter thereof is finished to a predetermined size with a small-diameter hole of the ferrule as a center of this processing. In this step, both ends of the funnel type ferrule are supported by two conical-shaped centers and then the ferrule is rotated to grind the outer peripheral surface thereof. Thus, if there is a difference in shape accuracy (e.g., circularity) between the small-diameter hole and the large-diameter hole, support points of both the centers cannot be set in the center of each of them, so that a deviation in axis occurs between the large-diameter hole and the small-diameter hole, thereby deteriorating connecting performance of the ferrule.
Therefore, an object of the present invention is to provide a ferrule for optical connectors which has been improved to solve the above described problem of the funnel type optical connector ferrule.